
[Sponsors] 
Wrong fluctuation of pressure in transient simulation 

LinkBack  Thread Tools  Search this Thread  Display Modes 
February 28, 2015, 00:46 
Wrong fluctuation of pressure in transient simulation

#1 
New Member
Cai Tao
Join Date: Oct 2014
Location: China shanghai
Posts: 7
Rep Power: 8 
Hi.
I come across a problem in a transient simulation. I use the LES model to simulation a sequare cylinder, and set some pressure monitoring points. The results of the pressure have a strange fluctuation, which is shown in the follow pictures. the file of controDict // ************************************************** *********************** //libs ( ); application pisoFoam; startFrom latestTime; startTime 0; stopAt endTime; //stopAt writeNow; endTime 5; deltaT 5.0e6; writeControl timeStep; writeInterval 1000; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; functions { probes { type probes; functionObjectLibs ("libsampling.so"); enabled true; outputControl timeStep; outputInterval 1; probeLocations ( ( 0.06 0.02 0.08 ) ( 0.005 0.0095 0.08 ) ( 0.005 0.0305 0.08 ) ( 0.015 0.0095 0.08 ) ( 0.015 0.0305 0.08 ) } // ************************************************** *********************** // the file of fvScheme // ************************************************** *********************** // ddtSchemes { default backward; } d2dt2Schemes { } gradSchemes { default Gauss linear; grad(nuTilda) cellLimited Gauss linear 1; grad(U) cellLimited Gauss linear 1; } divSchemes { default none; div(phi,U) Gauss LUST unlimitedGrad(U); //div(phi,U) Gauss linearUpwind unlimitedGrad(U); div(phi,k) Gauss limitedLinear 1; div(phi,nuTilda) Gauss limitedLinear 1; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear limited corrected 0.33; } interpolationSchemes { default linear; } snGradSchemes { default limited corrected 0.33; } fluxRequired { default no; p; } // ************************************************** *********************** // the file of fvSolution // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver GAMG; tolerance 1e6; relTol 0.1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 40; cacheAgglomeration on; agglomerator faceAreaPair; nCellsInCoarsestLevel 128; mergeLevels 1; } pFinal { $p; tolerance 1e6; relTol 0; }; "(UkBnuTilda)" { solver smoothSolver; smoother GaussSeidel; tolerance 1e07; relTol 0.1; } "(UkBnuTilda)Final" { $U; tolerance 1e7; relTol 0; }; } PISO { nCorrectors 2; nNonOrthogonalCorrectors 5; pRefCell 0; pRefValue 0; } relaxationFactors { "U.*" 1; "p.*" 1; "nuTilda.*" 1; } // ************************************************** *********************** // part of the file of the log Time = 0.12566 Courant Number mean: 0.00839828 max: 0.310058 smoothSolver: Solving for Ux, Initial residual = 3.6145e05, Final residual = 1.33368e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.00041477, Final residual = 1.43826e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.00079561, Final residual = 3.29873e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00910454, Final residual = 0.000548275, No Iterations 1 GAMG: Solving for p, Initial residual = 0.002062, Final residual = 0.000200861, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00120839, Final residual = 9.88252e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000657611, Final residual = 6.04321e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334683, Final residual = 2.98511e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000201084, Final residual = 1.9542e05, No Iterations 3 time step continuity errors : sum local = 1.57267e11, global = 3.70403e14, cumulative = 2.7449e12 GAMG: Solving for p, Initial residual = 0.00336111, Final residual = 0.00018496, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00165023, Final residual = 0.0001041, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000837023, Final residual = 6.35304e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429824, Final residual = 4.20207e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000238282, Final residual = 2.09567e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144679, Final residual = 9.81141e07, No Iterations 80 time step continuity errors : sum local = 8.19777e13, global = 3.70403e14, cumulative = 2.70786e12 ExecutionTime = 6263.22 s ClockTime = 6361 s Time = 0.125665 Courant Number mean: 0.00839835 max: 0.310065 smoothSolver: Solving for Ux, Initial residual = 3.61455e05, Final residual = 1.33319e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414767, Final residual = 1.43823e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795566, Final residual = 3.29825e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00916193, Final residual = 0.0005405, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205039, Final residual = 0.00019946, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118592, Final residual = 9.89506e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000645054, Final residual = 6.05196e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332466, Final residual = 3.01745e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198621, Final residual = 1.98006e05, No Iterations 3 time step continuity errors : sum local = 1.59175e11, global = 6.0819e14, cumulative = 2.76868e12 GAMG: Solving for p, Initial residual = 0.00335465, Final residual = 0.000184149, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164526, Final residual = 0.000104069, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834565, Final residual = 6.34114e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428368, Final residual = 4.17622e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237407, Final residual = 2.04899e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.00014399, Final residual = 9.93928e07, No Iterations 77 time step continuity errors : sum local = 8.52212e13, global = 6.0819e14, cumulative = 2.8295e12 ExecutionTime = 6310.82 s ClockTime = 6409 s Time = 0.12567 Courant Number mean: 0.00839843 max: 0.310072 smoothSolver: Solving for Ux, Initial residual = 3.61467e05, Final residual = 1.33373e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414775, Final residual = 1.43828e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795495, Final residual = 3.29769e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0091657, Final residual = 0.00054717, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205872, Final residual = 0.000199804, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00120643, Final residual = 9.84e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000656809, Final residual = 6.01974e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334246, Final residual = 2.96852e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000200805, Final residual = 1.95013e05, No Iterations 3 time step continuity errors : sum local = 1.56932e11, global = 3.71509e14, cumulative = 2.79235e12 GAMG: Solving for p, Initial residual = 0.00336065, Final residual = 0.000184732, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164948, Final residual = 0.000103936, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000836544, Final residual = 6.33963e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429508, Final residual = 4.19258e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00023813, Final residual = 2.08646e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.00014451, Final residual = 9.97118e07, No Iterations 79 time step continuity errors : sum local = 8.31101e13, global = 3.71509e14, cumulative = 2.75519e12 ExecutionTime = 6358.9 s ClockTime = 6457 s Time = 0.125675 Courant Number mean: 0.0083985 max: 0.310079 smoothSolver: Solving for Ux, Initial residual = 3.61467e05, Final residual = 1.33325e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414768, Final residual = 1.43821e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.00079544, Final residual = 3.29733e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00908316, Final residual = 0.000539338, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00204978, Final residual = 0.000199266, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118581, Final residual = 9.87077e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000644816, Final residual = 6.03733e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332293, Final residual = 3.01533e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198653, Final residual = 1.98122e05, No Iterations 3 time step continuity errors : sum local = 1.59243e11, global = 6.10176e14, cumulative = 2.81621e12 GAMG: Solving for p, Initial residual = 0.00335482, Final residual = 0.000184184, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164542, Final residual = 0.000104145, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834698, Final residual = 6.35111e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428487, Final residual = 4.18969e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237558, Final residual = 2.06722e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144187, Final residual = 9.92679e07, No Iterations 79 time step continuity errors : sum local = 8.51382e13, global = 6.10176e14, cumulative = 2.87723e12 ExecutionTime = 6407.22 s ClockTime = 6506 s Time = 0.12568 Courant Number mean: 0.00839857 max: 0.310086 smoothSolver: Solving for Ux, Initial residual = 3.61473e05, Final residual = 1.33375e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414769, Final residual = 1.43821e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795392, Final residual = 3.29701e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00903316, Final residual = 0.000545484, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205756, Final residual = 0.000199936, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0012069, Final residual = 9.83739e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000657011, Final residual = 6.01633e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334339, Final residual = 2.97385e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000200948, Final residual = 1.94727e05, No Iterations 3 time step continuity errors : sum local = 1.56695e11, global = 3.72636e14, cumulative = 2.83997e12 GAMG: Solving for p, Initial residual = 0.00336013, Final residual = 0.000184686, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164964, Final residual = 0.00010392, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000836632, Final residual = 6.34008e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429559, Final residual = 4.19243e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000238137, Final residual = 2.08849e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144556, Final residual = 9.82253e07, No Iterations 79 time step continuity errors : sum local = 8.19351e13, global = 3.72636e14, cumulative = 2.8027e12 ExecutionTime = 6455.37 s ClockTime = 6554 s Time = 0.125685 Courant Number mean: 0.00839865 max: 0.310093 smoothSolver: Solving for Ux, Initial residual = 3.61477e05, Final residual = 1.33329e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414766, Final residual = 1.43816e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795332, Final residual = 3.29664e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00902425, Final residual = 0.000538001, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00204822, Final residual = 0.000198808, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118526, Final residual = 9.88807e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000645015, Final residual = 6.0607e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332475, Final residual = 3.02826e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198705, Final residual = 1.66574e05, No Iterations 4 time step continuity errors : sum local = 1.34104e11, global = 6.12341e14, cumulative = 2.86394e12 GAMG: Solving for p, Initial residual = 0.0033574, Final residual = 0.00018402, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164436, Final residual = 0.000103905, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834272, Final residual = 6.33415e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428371, Final residual = 4.17247e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237515, Final residual = 2.0474e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144517, Final residual = 9.88653e07, No Iterations 77 time step continuity errors : sum local = 8.48563e13, global = 6.12341e14, cumulative = 2.92517e12 ExecutionTime = 6500.77 s ClockTime = 6601 s actually， I have once slove this problem by change the mesh, see the post "A shock appears after several periods of the transient simulation"http://www.cfdonline.com/Forums/openfoamsolving/143751shock appearsafterseveralperiodstransientsimulation.html. but now, this method seems useless. Can someone come across such problem. maybe we can have a disscussion. 

February 28, 2015, 09:33 

#2 
Senior Member
anonymous
Join Date: Aug 2014
Posts: 205
Rep Power: 9 
Maybe you should let te simulation run for a lot more of time. I don't think that it has had enough time to settle.
If you've already tried it, we could dip in it further 

March 5, 2015, 22:33 

#3  
New Member
Cai Tao
Join Date: Oct 2014
Location: China shanghai
Posts: 7
Rep Power: 8 
Quote:
I have run this case form time 0.125s to 0.24s, and the result is still unsatisfactory. The attached pictures are the result. Do you think I need to keep runing this case? or maybe I need to change some sets? 

Tags 
pressure, transient simulation, wrong fluctuation 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Simulation of high pressure diesel injector  all phases compressible with cavitation  fivos  CFX  4  July 30, 2015 07:48 
the problem of my transient simulation "Floating point exception: Overflow "  alloveyou  CFX  15  November 22, 2012 12:14 
transient simulation of a rotating rectangle  icesniffer  CFX  1  August 8, 2009 08:25 
Pressure boundary in transient simulation  Nyatoto  CFX  0  June 27, 2003 08:27 
Hydrostatic pressure in 2phase flow modeling (long)  DS & HB  Main CFD Forum  0  January 8, 2000 16:00 